Whats more important - Weight Balance or Exit Angle?

[MNC]

...If the truck is tall then I'd go for high antisquat as that will help reduce weight transfer and keep the front wheels on the ground. And also improve high climb ability.

Thanks for the comments - can you please explain anti-squat to me. Cheers,

[Heath]

...If the truck is tall then I'd go for high antisquat as that will help reduce weight transfer and keep the front wheels on the ground. And also improve high climb ability.

Thanks for the comments - can you please explain anti-squat to me. Cheers,

Anti squat is a dislike of short people and dwarves.


Sorry couldnt help myself.

Squat if I remember right is when you give a squirt of power and the rear drops so anti squat would be the compensation or geometry to counter for this movement. From what I've read its a black art where magicians do stuff none of us mortals understand and the result is a machine that remains level and stable under power and braking.

[MNC]

Anti squat is a dislike of short people and dwarves.

I am a victim of this -

Squat if I remember right is when you give a squirt of power and the rear drops so anti squat would be the compensation or geometry to counter for this movement. From what I've read its a black art where magicians do stuff none of us mortals understand and the result is a machine that remains level and stable under power and braking.

OK, not sure this helps me at all... I'm fresh out of magic tricks

[rokhound]

Copied from a Pirate link.

QUESTION ASKED:
Just had a brainwave, or maybe just a brain fart. When is it better to have squat or when is it better to have anti squat? What works best for going up hill? I read that too much of one or the other will induce bouncing when climbing hills. Would it make any sense to build in an "on the fly" anti squat adjustment of some kind so that the postion of the upper link frame mount could be changed while driving? Or is there one particular amount of a/s that is perfect for everything? Is it 100%?
Adjustable mounts would require a bit of fabbing, but the quest for ultimate performance may make it worth while. Then again, I may be a blithering idiot.

And answer:
If you have more than 100% then as the power comes on the links will lift the rear up more than what the COG inertia effect will try to compress the rear springs. Now in this case if you apply enough torque suddenly the links will actually throw the rear of the chassis up into the air. As the chassis rises it gets to the point where it pulls the rear tyres off the ground - this causes them to spin and also removes the torque load out of the rear axle. So as there is not torque load on the rear axle the links no longer support the chassis so that the chassis begins to fall and lowers the tyres back to the ground. The spinning tyres again bit into the ground - get the torque load again - lift the chasis again and away we go - hopping like a mofo on the steep climbs. Im sure everybody has seen this effect. What you will find that if you rig does start to hop from too much AS then you can back off the throttle and reduce the size of the instant torque load so that you only lift the chassis slowly and smoothly then you can keep increasing the torque load back up to the full level without the rear starting to hop. BUT if you do start to get any wheel spin then the hopping will start again and again you have to back off the throttle and smoothly apply it again to keep the hopping under control. Again Im sure everybody has seen this effect.


Now if you have way less than 100% AS (say like 20%) then all that will happen is when you drop the clutch on the steep climbs you will get more wheel spinthat a rig that say has 60% AS but the rig will remain stable and it wont hop so you can just keep the boot in. The rig that has the more AS will hook up better and get a better initial launch when the power is suddenly brought on.

But to me the most important thing is for the rig to not to start hopping. Once you have a rig like this it is the most fun thing to drive because you can just lay into the throttle and keep it planted and just move the wheel back and forth trying to find the line that will keep you moving forward. And not having to back off the throttle cause the rig starts to hop.

This is why I think that as a first try at building a rear linked suspension that people should aim to get as low a AS level as they can so that the end result is a rear linked suspension that is stable and doesent hop. Also if you can build in some adjustability so that you can later increase the AS level if you think that you rig can handle it.

This is also why I dont think that finding the exact position of the COG or really trying to determine the exact AS percentage is necessary. Just try to make it as small as you can and then work you way to bigger AS levels.


http://www.pirate4x4.com/forum/showthre ... nk+dummies
There is a huge amount of info on Pirate about this, but essentially high anti squat numbers (100% plus) mean that if you lay into the throttle the rear end will squat down and bite in, which in turn will send the rear of the truck upwards until the load on the rear wheels releases, and then the arse end squats down again and so it goes on. This produces the dreaded wheel hop (SWB nisssans have huge issues with this). Low AS numbers however don't bite the drive in quite so hard, and allow the rear end to wheel spin a bit more. This reduces traction, but also stops wheel hop on hill climbing.
You can build AS adjustment into your link suspension design so then you can adjust it to where you are comfortable.
Mine POS has theoretical AS numbers of 54% (where I have it set currently), 82% and 110%. But until I can actually drive the new one I don't know which will be the best setup. The old rig had 70% odd AS and climbed very well, but it had very shitty IRC (instant roll centre) and COG (centre of gravity) numbers which meant it couldn't be driven at anything over 50kph.

[MNC]

Copied from a Pirate link.

http://www.pirate4x4.com/forum/showthre ... nk+dummies

There is a huge amount of info on Pirate about this, but essentially high anti squat numbers (100% plus) mean that if you lay into the throttle the rear end will squat down and bite in, which in turn will send the rear of the truck upwards until the load on the rear wheels releases, and then the arse end squats down again and so it goes on. This produces the dreaded wheel hop (SWB nisssans have huge issues with this). Low AS numbers however don't bite the drive in quite so hard, and allow the rear end to wheel spin a bit more. This reduces traction, but also stops wheel hop on hill climbing....

Cheers Rok Bit of Research for me to do

[Bulletproof]

Yeah me two. I didn't realise that fitting a v8 would totally stuff my rig, but then again I don't think richards would have a shit show in hell of driving where mine has gone.
I guess it must be a different strokes (or stroking) thing
Hmmmmmm ..........................

Where has yours gone ? Because I have done alot of the tuff tracks.

Cheers Richard

[rokhound]

Yeah me two. I didn't realise that fitting a v8 would totally stuff my rig, but then again I don't think richards would have a shit show in hell of driving where mine has gone.
I guess it must be a different strokes (or stroking) thing
Hmmmmmm ..........................

Where has yours gone ? Because I have done alot of the tuff tracks.

Cheers Richard

Touche

[rangimotors]

Yeah me two. I didn't realise that fitting a v8 would totally stuff my rig, but then again I don't think richards would have a shit show in hell of driving where mine has gone.
I guess it must be a different strokes (or stroking) thing
Hmmmmmm ..........................

Where has yours gone ? Because I have done alot of the tuff tracks.

Cheers Richard

hard to compare who's best when your driving different tracks/rocks I think this is a good example as to why you should build your rig to suit the sort of wheeling you want to do, not what suits the people on the internet or at the other end of the country.

[MNC]

hard to compare who's best when your driving different tracks/rocks I think this is a good example as to why you should build your rig to suit the sort of wheeling you want to do, not what suits the people on the internet or at the other end of the country.

Fair call, the idea of this thread was to get some ideas out there and understand the impact of rear diff location.

Before I started this thread I had intended to keep the rear diff as far forward as possible (to try and get more weight resting on rear wheels and less on the front). Based on alot of the comments made i've decided to move the rear diff further back mainly to improve climbing ability and stability.

I'm not trying to build the ultimate rig here (my budget would not allow that ) but since i'm doing some fairly major mods I really dont want to have to redo them later (when I find out my initial ideas were wrong). Best to learn a bit from the experienced guru's on this site

Cheers,

[rokhound]

hard to compare who's best when your driving different tracks/rocks I think this is a good example as to why you should build your rig to suit the sort of wheeling you want to do, not what suits the people on the internet or at the other end of the country.

Your'e quite right Rangi, and i should have stated it that way as well, but it pisses off when people who should know better out rate state that their line of thinking is the only way and everyone else is wrong. (apart from that the tracks are only a way to get to where the wheeling gets interesting )

Now MNC, read that pirate link at least 3 times and you will start to get the idea (and you will be able to pick out who knows what they are talking about).
Budget is not an issue with linked suspension as it will cost you the same amount to do it spot on or fark it up. (unless you are palying with coil overs).

[darinz]

Anti-squat is a black art and you can go onto Pirate and get the same info that says the complete opposite!
IMO the important thing is to keep it netrual.

If you have around 100% then they guys that seem to know what they are taling about say that is nuetral. ie below 100% is squat and above is anti-squat.

That been said, there are many cases of trucks that perform very very well that are to the extremes.

Contrary to what some people will tell you, there is no perfect number. Antisquat is just one more thing you need to take into account. It is not the holy grail. Actual weight balance, wheelbase, cog etc all come into play so when you read an extract from one discussion it can be misleading. If you read a lot, and make sure those talking aren't biased, then you start to get an understanding of what will and won't work for the type of driving you do.

GQ's with a lift have well over 100% anti-squat. They don't wheel hop they just loose traction.

If you take the assumptions made in the Pirate link, then you would set all trucks with as much squat as possible as they would handle better and there are no disadvantages to it. This is not the case so be careful when making decisions based upon some info that you read on the net!
I have read very very good discussion around AS% related to spring rate and the need to adjust AS% depending upon what you spring rate is.

The key is to understand and then relate that to real world experience to achieve a specific end goal.
A lot of discussion on Pirate is targeted at rock climbing and so doesn't cross over to the sort of 4x4 we do, so understand what and why they are saying things and then relate that to NZ.

This discussion is held every few months on Pirate and depending who gets involved the conclusions change! Also go onto RaceDezerts and they will have the same discussion (but targeted at Desert racing) and the outcome can be the same or completely different, BUT the discussions around Jeep Cherokee's are pretty good from a 4x4 point of view and are quite relative to our type of vehicles. ie what works for a moon buggy may not work on a 4x4 and may not work on a desert truck so be careful who you listen to.

I should add, antisquat will keep more traction on the front wheel but have less (relativelt speaking) on the rear. Mt old truck had too much squat for my liking as underpower the steering got very light and it was hard to steer. Take you foot off and the steering came back. My new one is being designed to maintain steering under power. (to a point)
So what is more imporant?

[MNC]

I should have never asked - more confused now than ever.

New strategy - Put it together where it looks to make sense (based on readings from Priate site) - drive it - change it if it doesn't work.

[darinz]

If you do some homework and get a basic understanding then that is probably enough to sure you keep it within what will work. Don't go too extreme and keep it within the arguments and you'll be fine. Lets face it, if people argue about certain ranges and you are within them, it SHOULD work!

[rokhound]

If you do some homework and get a basic understanding then that is probably enough to sure you keep it within what will work. Don't go too extreme and keep it within the arguments and you'll be fine. Lets face it, if people argue about certain ranges and you are within them, it SHOULD work!

That sounds like an idea. As you stated above, build and have a go. As I said, the hard costs are not that great, and worse case scenario is that you will need to alter link locations and lengths. The expensive bits (rod ends, bushes, hiems, coils, shocks etc) are not a throw away because of that. There will be considerable time involved though, so it all depends on what you value that at .

Keep a build thread going with it as well, with pics.

[Bulletproof]

There is no real rocket science about it.

What causes wheel jump ?

As the power comes on and the wheels suddenly turn forward the diff head wants to go backwards. In the process because the leaf springs are fixed at the front the whole truck tries to lift. The truck jumps up in the air with the wind up and traction is lost and a cycle sets in. The same thing happens with coils

An Anti tramp rod helps to fix this but the length of the rod needs to be right so that the diff stays on the same plain at all times as the diff goes up and down.

It is also important to have good shock absorbers as well.

You have to be quite a way out to cause big trouble.

Cheers Richard

[MNC]

There is no real rocket science about it.

What causes wheel jump ?

As the power comes on and the wheels suddenly turn forward the diff head wants to go backwards. In the process because the leaf springs are fixed at the front the whole truck tries to lift. The truck jumps up in the air with the wind up and traction is lost and a cycle sets in. The same thing happens with coils

An Anti tramp rod helps to fix this but the length of the rod needs to be right so that the diff stays on the same plain at all times as the diff goes up and down.

It is also important to have good shock absorbers as well.

You have to be quite a way out to cause big trouble.

Cheers Richard

How does the same thing happen with coils if the 4 link is fixed top and bottom of the diff?

[Bulletproof]

Sorry I have misled you there.

It won't do it with a 4 link setup but if people run an arm more like a prado of safari it can with coils because the angle of the diff alters as it rises and falls. Especially when the bushes flog out.

A 3 or 4 arm set up should hold the diff constant and give no trouble as long as the shocks are good.

Cheers Richard

[turoa]

Links will hop if you have too much antisquat. This is caused by the diff trying to drive under the vehicle when it gets traction, losing it and skidding back out again and the process repeats.

[rokhound]

Exactly Tu's. Which is why swb lifted rigs have mad arse wheel hop while climbing (as a rule).

Richard has it mostly right as long as you are playing with cart springs or factory c arm and panhard setups it isn't rocket science, but as Turoa has stated it can still happen with 4 link setup (and then it can be a real science!)

If you are trying to get it all together in your head in one go, it will fark you over , so just build it the way you want, remembering the rule of thumb is make your links as long as you can (sensibly), top links should work out at about 70-85% of the bottom ones (this is the most common way to do it anyway), vertical separation of the link mounts at the axle should be about 25% of the tyre size you are using, and build in some adjustment at the top link mounts at the chassis end.
If you use hiems (or similar) joints at one end, this will allow you to fine tune link lengths so that everything can be made to track straight etc.

[Bulletproof]

The diff on my truck stays in the same position and angle at all times.

The drive shaft only slides in and out 10mm max and only the wheels go up and down. So there is no axle tramp whether under power or shutting off and that is the secret of traction because there is no axle hop.

Cheers Richard

[wopass]

Exactly Tu's. Which is why swb lifted rigs have mad arse wheel hop while climbing (as a rule).

If you are trying to get it all together in your head in one go, it will fark you over , so just build it the way you want,

funny.. thats exactly what i did and it seems to work so it cant be that difficult cos i did all mine by eye'ometer fcuk the calcs

:edited to get around the fcuking swearword filter

[rokhound]

The diff on my truck stays in the same position and angle at all times.

The drive shaft only slides in and out 10mm max and only the wheels go up and down. So there is no axle tramp whether under power or shutting off and that is the secret of traction because there is no axle hop.

Cheers Richard

And that is the beauty of cart springs, a good traction bar and not having masses of wheel travel, but that is not what MNC is asking about, he is looking into a 4 link system (well that is the way this thread appears to have gone anyway)

[Fakey]

And that is the beauty of cart springs, a good traction bar and not having masses of wheel travel, but that is not what MNC is asking about, he is looking into a 4 link system (well that is the way this thread appears to have gone anyway)

By the sounds of it hes goin for a pretty close to standard 80series setup in the rear now

[MNC]

By the sounds of it hes goin for a pretty close to standard 80series setup in the rear now

Standard 80 series diff but with custom arms and coils

[MNC]

funny.. thats exactly what i did and it seems to work so it cant be that difficult cos i did all mine by eye'ometer fcuk the calcs

:edited to get around the fcuking swearword filter

Hahaha!

[Bulletproof]

And that is the beauty of cart springs, a good traction bar and not having masses of wheel travel,

I personally don't believe a person needs lots of wheel travel for ordinary 4 wheel driving. I have 7-800mm and I think with diff locks that is plenty.

I have done quite a bit with the jalopy with extreme wheel travel and I think the big footprint probably makes most of the difference. Jafa may disagree but that is my observation. Hard tracks like Waitawheta you dont need excess wheel travel and there are lots of track like that.

Rock crawling is a different ball game.

Cheers Richard

[mudlva]

And that is the beauty of cart springs, a good traction bar and not having masses of wheel travel,

I personally don't believe a person needs lots of wheel travel for ordinary 4 wheel driving. I have 7-800mm and I think with diff locks that is plenty.

I have done quite a bit with the jalopy with extreme wheel travel and I think the big footprint probably makes most of the difference. Jafa may disagree but that is my observation. Hard tracks like Waitawheta you dont need excess wheel travel and there are lots of track like that.

Rock crawling is a different ball game.

Cheers Richard

Yip second that thought
lockers will generally outdrive soft suspension and long traveling wheels except when they too are locked.
my lwb truck with lockers weight is about 55/45 heavier on the rear axle can have two opposite wheels hanging off the ground and i can move forward and rearwards to help align the truck for the next stage / hazards section.
when the front was a lot heavier then the rear the nose would always "fall" into the hole generally meaning that the winch was needed to extract me as team recovery was generally limited due to the terrain that we were all in etc

just my thoughts

[darinz]

Well I just wrote my next article, thanks for the motivation guys!

[MNC]

Exactly Tu's. Which is why swb lifted rigs have mad arse wheel hop while climbing (as a rule)....

...If you are trying to get it all together in your head in one go, it will fark you over , so just build it the way you want, remembering the rule of thumb:

1. Make your links as long as you can (sensibly),
2. Top links should work out at about 70-85% of the bottom ones (this is the most common way to do it anyway),
3. Vertical separation of the link mounts at the axle should be about 25% of the tyre size you are using, and
4. Build in some adjustment at the top link mounts at the chassis end....

Quote edited by MNC...

OK, so I have been trying to get my head around this and your second sentence above was correct

1. Top links approx 720mm & Bottom approx 1000mm
2. See above - works out at 72%
3. Separation is 390mm which is approx 39% of tyre size.
4. Adjustment... nope none here Not much option given fuel tank is in the way.

What do you reckon???

I've plugged the numbers into the 4 link calc but it seams to change completely depending on what Vehicle Centre of Gravity Height I make up (yes I said make up - you should see the calculation to work this VCOGH out ).

With VCOGH at 42" I get 100% Anti-squat (changed VCOGH until I got 100%).
If it was actually 34" (what the program defaults to my Anti-squat would be 126%





I'm getting a bit over this so think it'll just get welded in as is unless anyone has a usefull suggestion (one time only offer - after tonight no changes will be made and no correspondence entered into bla bla bla...).

[meatc]

Centre of gravity can make a big difference which is why its in the calculator.

After much reasearch when I did mine I found the general concensus for COG was top bell housing bolt height from ground.

just a guide but might be worth looking at before you break out the welder. I ended up estimating mine off the calcs and it seems to work well. I know of one who busts rear diffs every time he gases it up a decent climb and it axle tramps like you wouldn't believe. He is about to rip it to bits and start again.

If you are using 80 series all round aim for factory angles and seperation.

My 2c